Motorola ts907 low hv

[Yamamaya42]

Originally Posted by timmy

Ok so I have a theory the high voltage across L42 my theory is that the voltage on the path of the 470pf cap which goes to v6 as well as the 2.2 cap coming off the agc pot both those voltages come from the flyback so if infact there is still a problem with v6 then I think it’s safe to say the tube is not conducting correctly if any at all because if it were conducting then I think it would relieve excessive voltage at L42 because right now it appears to be solid standing voltage on both sides of L42 780v. That may explain why removing one lead from each cap having no change and still heating L42. Which in turn possibly shutting down v1 having no snow on screen and no video.

That is not how it works.
The AGC circuit does not take any voltage away from there via C59, it does take filtered horizontal pulses from the FBT, any DC is blocked by C59.

That lower winding on the FBT serves more than one function, one of them is generating +/- 500v AC horizontal pulses AND the boost voltages, pin 9 being the pin where power is fed in.

ALL PINS are at DC boost potential in the focus circuit, this is normal.
As there is no diode used in this boost setup, no matter where you measure, you will see boost level voltage in this area.

So there is no “excessive voltage on both sides of L42” the entire area is at 780v DC and this is normal.

What is causing it to heat is the AC pulses it's getting and nothing with any DC voltage in the circuit.